1. Field of the Invention
The present invention relates to a spatial light communication equipment for spatially transmitting optical signals and more particularly to the spatial light communication equipment which can be used suitably for ultra-long-distance spatial optical communications such as intersatellite optical communications.
The present application claims priority of Japanese Patent Application No.2000-011338 filed on Jan. 20, 2000, which is hereby incorporated by reference.
2. Description of the Related Art
An information transmitting system using optical signals includes, in addition to a wired transmission system through an optical fiber being featured by non-inductive, low-loss and wide-band optical transmission, a spatial transmitting system using spatial light such as infrared rays. The spatial transmitting system, though it is of lower quality of transmission than the wired transmission system, can provide low-cost and highly practical communication simply by installing a spatial light communication equipment enabling communication by spatial light on transmitting side and receiving side within an unobstructed spatial range. The spatial transmission system is very advantageous in ultra-long-distance communication which costs much to install wired transmission lines such as optical fibers and/or in intersatellite optical communications in which installation of wired transmission lines is impossible, in particular.
To carry out communications using spatial light, the spatial light communication equipment installed on a transmitting side is placed opposite to one installed on a receiving side and a spatial light receiving communication equipment (hereinafter may be referred to as a receiver) receives spatial light emitted by a spatial light transmitting communication equipment (hereinafter may be referred to as a transmitter). In the case of intersatellite optical communications being ultra-long-distance communication, since the spatial light to be emitted is a light beam having directivity as sharp as about 10xcexc rad, seizure/tracking capability and beam directivity with accuracy of about 1 xcexcrad are required to receive the emitted beams of light.
FIG. 8 is a schematic block diagram for showing configurations of a conventional spatial light communication equipment. In this spatial light communication equipment, communications are carried out by using transmitting and receiving beams which are transmitted or received on a same optical axis between the transmitter and the receiver. A beam emitted from the transmitter (not shown) is received by an optical antenna 10 of the receiver. The beam received by the optical antenna 10 is transmitted to a beam deflector 11. The beam deflector 11 totally reflects only the beam received through the optical antenna 10 and guides it toward a beam splitter 12. On an optical axis of the beam totally reflected by the beam deflector 11 are placed the beam splitter 12, a beam splitter 13 and an angle detector 14. The beam splitter 12 allows the beam totally reflected by the beam deflector 11 to pass through itself. The beam splitter 13 allows the beam transmitted through the beam splitter 12 to pass through itself and then outputs the beam to the angle detector 14 and, at a same time, guides the beam toward an optical receiver 15. The angle detector 14 detects an angle of deviation, relative to an optical axis of the beam totally reflected by the beam deflector 11, of the beam transmitted through the beam splitter 13. The optical receiver 15 converts the beam guided by the beam splitter 13 to an electrical signal and performs predetermined signal receiving processing.
On the other hand, since direction in which the optical antenna 10 is directed to the spatial light communication equipment (not shown) installed on the opposite side is displaced by an angle of deviation detected by the angle detector 14, a transmitting signal to be transmitted to the receiver is emitted with the angle of deviation being corrected. At this point, transmitting signal to be transmitted by an optical transmitter 16 is converted to an transmitting beam as an optical signal and is output to the beam splitter 12. The beam splitter 12 guides the transmitting beam fed by the optical transmitter 16 toward the beam deflector 11. The beam deflector 11, by using a control section (not shown), is adapted to improve signal receiving sensitivity of the optical receiver 15. The beam deflector 11 also controls a deflected angle depending on angle of deviation detected by the angle detector 14 so that a direction of the transmitting beam fed by the optical antenna 10 directed to the receiver is corrected by the angle of deviation. The beam deflector 11 totally reflects the beam fed from the beam splitter 12 and guides it toward the optical antenna 10. The optical antenna 10 transmits the beam from the beam deflector 11 to the receiver.
Thus, in the spatial light communication equipment by which communication is carried out by transmitting and receiving the beam on the same optical axis between the transmitter and receiver, by controlling an angle of the beam deflected by the beam deflector 11, the corrected angle detected at a time of tracking the receiving beam is applied to adjustment of directions of the transmitting beam. This enables sharp directivity of beam light in the spatial light communication equipment to be implemented, with simplified configurations.
FIG. 9 is a schematic block diagram showing configurations of a conventional spatial light communication equipment in which communication is carried out using signal transmitting and receiving beams being transmitted on different optical axes. The spatial light communication equipment of this type is provided with one optical antenna for transmitting beams and another optical antenna for receiving beams to carry out communication using beams to be transmitted and received on the different optical axes between the transmitter and receiver. Therefore, a receiving beam transmitted from the transmitter is received by a signal receiving optical antenna 20. The receiving beam received by the signal receiving optical antenna 20 is output to a beam deflector 21. The beam deflector 21 totally reflects only the receiving beam fed from the signal receiving optical antenna 20 and guides them toward a beam splitter 22. On an optical axis of the receiving beam totally reflected by the beam deflector 21 are placed the beam splitter 22 and an angle detector 23. The beam splitter 22 allows the receiving beam totally reflected by the beam deflector 21 to pass through itself to output to the angle detector 23 and, at a same time, guides the beam toward an optical receiver 24. The angle detector 23 detects an angle of deviation, relative to an optical axis of the beam totally reflected by the beam deflector 21, of the beam transmitted through the beam splitter 22. The optical receiver 24 converts the beam guided by the beam splitter 22 to an electrical signal and performs predetermined signal receiving processing The spatial light communication equipment shown in FIG. 9 is provided with a control section (not shown) adapted to change the angle deflected by the beam deflector 21 depending on the angle of deviation of the transmitted light beam detected by the angle detector 23 in order to improve signal receiving sensitivity of the optical receiver 24. An amount of the corrected angle changed by the control section is monitored by an angle transferring circuit 25 and is transferred, with high accuracy, to a beam deflector 26.
A transmitting signal to be transmitted from the spatial light communication equipment is converted to an optical signal by an optical transmitter 27 and is output to the beam deflector 26. The beam deflector 26 totally reflects only specified beam component in the transmitting beams and guides them to a mirror 28. The mirror 28 guides the transmitting beam totally reflected by the beam deflector 26 toward a signal transmitting optical antenna 29. The signal transmitting optical antenna 29 transmits out the transmitting beam totally reflected by the mirror 28 to a receiver (not shown).
Thus, in the spatial light communication equipment by which communication is carried out by transmitting the signal transmitting and receiving beams on the different optical axes between the transmitter and receiver, by controlling the angle of the beam deflected by the beam deflector on the beam receiving side based on the corrected angle corresponding to results from tracking of receiving beams, the controlled amount of the corrected angle is applied, with high accuracy, to adjustment of directions of the transmitting beam by the beam deflector. This enables highly accurate tracking capability of the receiving beam and sharp directivity of the transmitting beam to be implemented.
However, in the conventional spatial light communication equipment shown in FIG. 8, since communication is carried out by transmitting and receiving beams on the same optical axis, identification between the transmitting beam and receiving beam is generally made by a wavelength or a direction of a polarized wave. Therefore, when the identification is made by the wavelength, if, in one spatial light communication equipment, a beam of light having a wavelength of xcex1 is used as the transmitting spatial light to be transmitted and a beam of light having a wavelength of xcex2 as the receiving spatial light to be received, in the other spatial light communication equipment, the beam of light having a wavelength of xcex2 and the beam of light having a wavelength of xcex1 must be used as the transmitting spatial light and as the receiving spatial light respectively. That is, since one spatial light communication equipment cannot be used as a substitute for the other, it is impossible to maintain compatibility.
Moreover, to implement the compatibility between the two spatial light communication equipments disposed opposite to each other, since the transmitting beam and receiving beam use a beam of light having same wavelength or same polarized wave, a filter to separate a wavelength component and a polarized wave component contained in the light same wavelength and polarized wave has to be additionally installed. To carry out ultra-long-distance spatial light communications, a dynamic range between a transmitting spatial light level and a receiving spatial light level of the spatial light communication equipment has to be widened. However, when the filter for separation of the wavelength component and polarized wave component is mounted, since a crosstalk of the transmitting spatial light in the spatial light communication equipment cannot be removed due to unavoidable factors such as feedback light, it becomes impossible to widen the dynamic range.
On the other hand, in the conventional spatial light communication equipment shown in FIG. 9, since communication is carried out by transmitting and receiving beams on different optical axes, it is possible to ensure compatibility between two spatial light communication equipments disposed opposite to each other. However, a beam deflector for a receiving beam and a beam deflector for a transmitting beam have to be installed separately and, after having detected an amount of corrected angle in tracking of the receiving beam, control has to be made so as to transfer, with high accuracy, the amount of the corrected angle to the beam deflector for the transmitting beam, thus causing complicated control configurations and an increased size of the conventional spatial light communication equipment.
In view of the above, it is an object of the present invention to provide a spatial light communication equipment being capable of providing compatibility between two spatial light communication equipments placed opposite to each other and of providing, with simplified configurations, highly accurate seizure and tracking capability and excellent beam directivity for ultra-long-distance communication.
According to a first aspect of the present invention, there is provided a spatial light communication equipment including:
a first optical antenna to receive receiving spatial light from a spatial light communication equipment installed on an opposite side;
a angle detector for detecting an angular error from a specified signal receiving optical axis from the receiving spatial light received by the first optical antenna;
a controller (correcting means) for correcting, based on the angular error detected by the angle detector, the angular error of the receiving spatial light from the specified signal receiving optical axis and angular error of transmitting spatial light to be emitted to the spatial light communication equipment installed on the opposite side; and
a second optical antenna to transmit the transmitting spatial light whose angular error has been corrected by the controller (correcting means).
In the above configuration, the angular error of the receiving spatial light emitted from the spatial light communication equipment installed on the opposite side and received by the first optical antenna, from the specified signal receiving optical axis, is detected and the angular error of the receiving spatial light and the angular error of the transmitting spatial light to be emitted to the spatial light communication equipment installed on the opposite side are corrected by the controller (correcting means). Polarity of the transmitting spatial light whose angular error has been corrected is reversed by the second optical antenna and is transmitted to the spatial light communication equipment installed on the opposite side.
With the above configuration, since an amount of the angular error of the receiving spatial light is used for controlling direction of the transmitting spatial light, the spatial light communication equipment in which both tracking and seizure of the receiving spatial light and the control on the direction of the transmitting spatial light are made possible, with simplified structures, can be implemented.
According to a second aspect of the present invention, there is provided a spatial light communication equipment including:
a first optical antenna to receive receiving spatial light from a spatial light communication equipment installed on an opposite side;
a beam deflector having a first reflecting plane to deflect the receiving spatial light received by the first optical antenna on a specified optical axis;
an angle detector for detecting an angular error of the receiving spatial light deflected on the specified optical axis;
a controller for correcting, based on the angular error detected by the angle detector, an angle deflected by the beam deflector;
a reflector for guiding transmitting spatial light toward the specified optical axis of the receiving spatial light to be emitted to the spatial light communication equipment installed on the opposite side, corrected by the controller and reflected by a second reflecting plane being positioned on a back-surface of the first reflecting plane of the beam deflector; and
a second optical antenna to reverse a polarity of the transmitting spatial light reflected by the reflector and to transmit the transmitting spatial light to the spatial light communication equipment installed on the opposite side.
In the above configuration, the angular error of the receiving spatial light fed from the spatial light communication equipment installed on the opposite side and received by the first optical antenna is detected after having been deflected on the specified optical axis by the first reflecting plane of the beam deflector and then the deflected direction is corrected by the controller. The transmitting spatial light to be emitted to the spatial light communication equipment installed on the opposite side is reflected by the second reflecting plane of the reflector which is positioned on the back-surface of the first reflecting plane of the beam deflector whose deflecting direction has been corrected by the controller and is then guided toward the specified optical axis of the receiving spatial light by the reflector and is transmitted, with its polarity reversed by the second optical antenna, to the spatial light communication equipment installed on the opposite side.
With the above configuration, a spatial separation between the signal transmitting and receiving beams within the spatial light communication equipment and complete blocking of invasion of crosstalk of the transmitting beam into the signal receiving system can be achieved, with very simplified configurations, thus implementing a spatial light optical communication system requiring no considerations about allotment of wavelength component and/or polarized wave component. Also, by transmitting the signal transmitting and receiving beams on different optical axes, light having a same wavelength and same polarized component can be used between the transmitter and receiver, thus ensuring compatibility of the spatial light communication equipment.
Furthermore, by using both the surface reflecting plane and rear reflecting plane of the beam deflector, the deflected angle to be corrected can be transferred under a well controlled condition, enabling highly accurate tracking and seizure capability and controlled directivity of the signal light. Therefore, the spatial light communication equipment can be used for ultra-long-distance spatial optical communications requiring highly accurate tracking and seizure capability and controlled directivity of the signal light such as the intersatellite optical communications. By incorporating a light source having a high signal transmitting level and an optical receiver having high signal receiving sensitivity into the spatial light communication equipment, very excellent intersatellite optical communication system can be constructed.
According to a third aspect of the present invention, there is provided a spatial light communication equipment including:
a first optical antenna to receive receiving spatial light from a spatial light communication equipment installed on an opposite side;
a beam deflector having a first reflecting plane to deflect the receiving spatial light received by the first optical antenna on a specified optical axis;
an angle detector for detecting an angular error of the receiving spatial light deflected on the specified optical axis;
a controller for correcting, based on the angular error detected by the angle detector, an angle deflected by the beam deflector; and
a second optical antenna having a polarity being opposite to that of the first optical an antenna including a concave lens to expand a diameter of the transmitting spatial light to be emitted to the spatial light communication equipment installed on the opposite side, corrected by the con-roller and reflected by a second reflecting plane being positioned on a back-surface of the first reflecting plane of the beam deflector, a reflector to guide the transmitting spatial light whose diameter has been expanded by the concave lens toward the specified optical axis of the receiving spatial light and a convex lens to collimate the transmitting spatial light reflected by the reflector and to transmit out the transmitting spatial light.
In the above configuration, the second optical antenna is so configured that the reflector to guide the transmitting spatial light toward the specified optical axis of the receiving spatial light is disposed between a Galileian-type concave lens used to reverse polarity of the transmitting spatial light and to expand beam diameter and the convex lens to collimate the transmitting spatial light.
With the above configuration, since the concave lens making up the second optical antenna is disposed as near to the second reflecting plane of the beam deflector as possible, the reflected light can be handled in vicinity of a center area where aberration of the concave lens is small and further its lens diameter can be made smaller. Therefore, transmitting accuracy of the transmitting spatial light can be improved and size of the spatial light communication equipment itself can be made smaller.
According to a fourth aspect of the present invention, there is provided a spatial light communication equipment including:
a first optical antenna to receive receiving spatial light from a spatial light communication equipment installed on an opposite side;
a beam deflector having a first reflecting plane to deflect the receiving spatial light received by the first optical antenna on a specified optical axis;
an angle detector for detecting an angular error of the receiving spatial light deflected on the specified optical axis;
a controller for correcting, based on the angular error detected by the angle detector, an angle deflected by the beam deflector;
a second optical antenna to reverse a polarity of transmitting spatial light to be emitted to the spatial light communication equipment installed on the opposite side, corrected by the controller and reflected by a second reflecting plane being positioned on a back-surface of the first reflecting plane of the beam deflector, and
a reflector to guide the transmitting spatial light transmitted by the second optical antenna toward the specified optical axis of the receiving spatial light.
In the above configuration, the angular error of the receiving spatial light fed from the spatial light communication equipment installed on the opposite side and received by the first optical antenna is detected after the receiving spatial light has been deflected on the specified optical axis by the first reflecting plane of the beam deflector and deflected direction is corrected by the controller. Then, the transmitting spatial light to be transmitted to the spatial light communication equipment installed on the opposite side is reflected by the second reflecting plane being the back-surface of the first reflecting plane of the beam deflector whose deflecting direction has been corrected by the controller and, after its polarity is reversed by the second optical antenna and is emitted, is guided to the specified optical axis of the receiving spatial light by the reflector.
With the above configuration, since the lens making up the second optical antenna is disposed as near to the second reflecting plane of the beam deflector as possible, the reflected light can be handled in vicinity of a center area where aberration of the lens is small and further its lens diameter can be made smaller. Moreover, since commercially available signal transmitting optical antenna can be appropriated, costs for the spatial light communication equipment can be reduced.
In the foregoing, a preferable mode is one wherein the first optical antenna and the beam deflector are so disposed that an exit pupil of the receiving spatial light received by the first optical antenna is positioned on the first reflecting plane of the beam deflector.
In the above configuration, since the exit pupil of the receiving spatial light received by the first optical antenna is disposed on the first reflecting plane of the beam deflector, the specified optical axis deflected by the beam deflector can be held in a constant position.
With the above configuration, very highly accurate control on the spatial light can be achieved.
Furthermore, a preferable mode is one wherein the first and second optical antennas are operated under a same magnification and they receive and transmit spatial light having a same diameter.
In the above configuration, since the diameter of the spatial light transmitted and received by each of the first and second optical antennas is the same, compatibility between the transmitter and receiver can be further improved.